1. Field of the Invention
This invention relates to a device which uses refractive and fluorescence means to intensify, (1) photophosphorescence in a fiber marker with luminescent properties for use in marking systems and (2) fluorescence to create an emissions detector for laser or light dispersion flux fields.
2. Description of the Prior Art
The prior art using material with photophosphorescence to create luminescent markers has involved incorporating a phosphor in a synthetic resin such as polyethylene (Susuke--3,908,055) to form tiles, plates and spheres for use as inserts to form a luminous marker. This method of using phosphors for luminescent markers has the disadvantage of being inefficient use of the phosphor.
The method common to the trade of making material for luminescence markers by incorporating a phosphor in a binder and forming this luminous material into shapes, such as titles, plates and spheres, is not an effective use of the phosphor. An example of this method is the use of a calcium sulfide phosphor in a polyethylene binder to make a resin composite. Inserts made of this resin composite, in the form of tiles, are used to create a luminous road marker by embedding the tile in or to the pavement,
The advantage noted in the prior art is that it provides continuous luminous action through the exposing of new luminescence material as the marker abrades. However this method is not effective and is a disadvantage because phosphors are very detrimentally affected by moisture, salts and acids normally associated with weathering.
What occurs on the surface of this type of luminescence marker, on exposure to weather, is the loss by errosion of the phosphor particles in direct contact with the surface. The depth of moisture penetration into the luminescence marker will depend on the permeability of the binder resin used and how effective the individual phosphor particles are encapsulated within the binder. Interconnection between the phosphor particles will promote deep penetration of moisture through capillary action.
The moisture creates an opaque screen of inactivated phosphor particles between the marker surface and the underlying effective phosphor particles. This opaque screen is a boundary condition resulting from the direct exposure of the phosphor-resin composite to weather. The abrading of the surface will only result in the consumption of the marker and the inward movement of the opaque screen.
The phosphor inefficiency arise from the interference in the transmission of photons across the boundary between the phosphor molecules in the luminescence marker and the exposed marker surface. For photophosphorescence to occur, the phosphor molecule must be excited by visible or invisible light, a photon. After a delay, the phosphor molecule emits a photon at a longer wave length than the exciting photon. Obviously the emitted photon must be in the visible light region of the electromagnetic spectrum to be useful as a marker to the public. Therefore, the material between the emitting phosphor molecule and the surface of the marker must be translucent to permit the passage of light. The interference with the transmission of the exciting and emitting light to and from the active phosphor particles by the opaque screen of weathered material in exposed phosphor-resin composite inserts is one cause resulting in the ineffective use of the phosphor in markers of this type.
Interference to the transmission of the excitation energy and the luminescence is also created by the active phosphor particles which are opaque. The prior art has attempted to minimize the loss of translucency due to the opaque nature of the phosphor particles by using a transparent binder. One prior art method is the form a suspension of phosphor particles in a clear acrylic ester resin deposited on supporting sheets. (Hinson 3,005,103). Another prior art method is the use of small spheres coated with a phosphorescent material to activate fluorescent pigments in a transparent binder to provide a reflective colored return at night. (de Veries--3,253,146) (Gravisse--4,208,300).
Use of a clear binder to suspend the phosphor over a reflective film, or as phosphor coated spheres in a transparent binder, is the current commercial method of minimizing the opaque effect of phosphor. The method is to arrange the phosphor particles in a suspension to provide light pathways that enhance the return of the emitted light by clear binders and reflective backing film. Older methods simply maximize the amount of phosphor particles in the exposed surface.
In both approaches, the net effective emission surface is approximately half the surface receiving the excitation energy. To illustrate, consider a perfect uniform layer of phosphor one molecule thick on a horizontal plane being bombarded from overhead by photons that supply the excitation energy. The direction of the emission photons will be completely random, with the result half the emitted photons will travel below the horizontal plane, and half the emitted photons will emerge above the plane. The photons emerging below the plane can be directed by reflection back through spaces in the phosphor layer, but not through the phosphor molecules because of the opaque characteristic of the phosphor. The limiting effect in the production of lumination arises as more passageways are created to permit the return of the backscatter photons emitted below the plane, less phosphor molecules are available to generate the photons being reflected. Therefore, current commercial luminescent markers have the disadvantage of either losing half the emitted light to internal absorption by the marker body, or only capturing part of the excitation energy because of the need for creating voids in the phosphor surface to allow passage of the reflected light back in the direction of the marker surface.
Another disadvantage of prior art is the lack of mechanism to intensify the photophosphorsence lumination. Note that in this invention, phosphorescence is used to denote photons emitted by a molecule's electron return from a triplet state to the ground state. In general, photophosphoresence is delayed light emission associated with a change in electron spin. Fluorescence is the photon emitted by a molecule's electron return to the ground state from the singlet state.
Phosphorescence lumination is characterized by very low light intensities. For example, a zinc sulphide phosphor luminance one minute after excitation is 0.17 candles/m.sup.2 (c/m.sup.2) and 0.001 c/m.sup.2 after 30 minutes. For comparison, the luminance from a clear sky is approximately 3200 c/m.sup.2 and from white paper in moonlight is 0.03 c/m.sup.2. The prior art has no provisions for increasing the intensity of the phosphor luminance which results in photophosphorescence markers being useful primarily in night adapted vision situations.
Laser emission is characterized by a small diameter intense beam of photons with the same wavelength. The intensity of the laser beam makes detection a simple technical matter using a photoelectric detector cell based on amorphous silicon, monocrystal silicon or gallium-arsenic. However, the small cross-sectional area of the laser beam would require many detectors to assure a reasonable probability of detecting a rogue laser beam. For example, a blue-green laser passing thru water near a submarine would likely never be detected using known methods of prior art, because in the known prior art, the photoelectric surface must be in direct contact with the laser beam and also protected from damage by the intense laser flux of photons. This required protection of the photoelectric surface of necessity reduces the detector's sensitivity to the faint flux of dispersion photons scattered by the water, or air as the laser beam travels through the media.
Obviously, the laser photons can excite a fluorescent material with an excitation band in which the laser emission wavelength falls. In my invention, a fluorescent material that the laser emission can cause to fluorescence is referred to by the symbol of LEF-Dye.